In conventional cutting of rods, massive or tubular shapes made of metal materials such as steels, copper alloys, or aluminum alloys, the so-called metal sawing machine which is provided with a saw edge along a longitudinal end face of a band steel sheet made of carbide tool steel or alloy tool steel, is used.
The processing mechanism is not grinding, but is cutting, so that it is impossible to cut hard and brittle materials such as ceramics, glass, quartz, metal base composite material, intermetallic compound, and hard metal.
In the method for cutting off these above-mentioned special rod, massive, or tubular materials, there are usually two methods, as follows.
One cutting method is a so-called outer peripheral circular edge cutting method wherein the work 2 is pressed to be cut against a disc grindstone 10-1 which is provided on its outer periphery with an abrasive and is rotated at high speed as shown in FIG. 7.
Another cutting method is the so-called inner peripheral circular edge cutting method wherein a grindstone disc 10-2 provided on the inner periphery with an abrasive layer having a doughnut shape, as shown in FIG. 8, is rotated at high speed. The workpiece 2 is inserted into the inner circle of the grindstone disc and is cut while being pressed against the inner periphery of the grindstone disc 10-2.
The outer peripheral edge cutting method permits so-called multiple cutting to provide high cutting efficiency, and one workpiece 2 may be simultaneously cut to the desired thickness into many parts by means of a plurality of disc grindstones 10-1 laminated at regular intervals through spacers. However, in this cutting with the outer peripheral circular edge, the cutting depth of the work is limited to about one-third the outer diameter of the disc, and if it is required to cut pieces of a further large size the cutting edge is deflected and bent backwardly during machining, whereby it is impossible to process or machine the work precisely.
Accordingly, when it is required to cut materials of large diameter, the diameter of the grindstone itself must be increased. The more the diameter of the grindstone is increased, the greater the problems such as run-out of the grindstone, lower running accuracy of the machine and the like.
On the other hand, in the inner peripheral circular edge cutting method, it is possible to cut the relatively large workpiece 2 in the extent of the inner circle of the grindstone at high precision because the grindstone disc is rotated while being held at its outer periphery. It is impossible, however, to obtain a great number of cut products at the same time on account of the construction of the apparatus, which reduces the lower cutting efficiency.
To eliminate the disadvantages in these two kinds of cutting methods, a multi-blade cutting method is employed in which a plurality of band steel sheets (the blades) held in parallel at regular intervals are attached to a frame under a constant tension and the frame is then to cut the work. This cutting method has been developed to cut hard and brittle materials for semiconductors at high precision and in large quantities.
In blade cutting, there are usually three kinds of cutting methods, one of which is cutting with a metal sawing machine provided with a saw edge on the side end face as stated above, and two other cutting methods respectively involving grinding with bonded abrasive grains and free abrasive grains.
The metal sawing machine is suitable for cutting metal materials generally, as already stated, and is not used to cut special materials.
In the grinding method with bonded abrasive grains, a chip composed of an abrasive layer, which is attached to a side end of a steel sheet, is usually used in rough-cutting of easy cuttable materials such as marbles, limestones, sandstones and the like.
However, for cutting of the above-mentioned hard and brittle materials at high precision, free abrasive grains are mainly used. The multi-blade cutting method with free abrasive grains is illustrated in FIGS. 9 to 12. A plurality of elongated blades 1' made of band steels of SK material and having a thickness of approximately 0.1 to 0.3 mm are disposed mutually in parallel at regular intervals through spacers 3 and secured to the frame 10 by means of a fixture 4. Then, a tensile force as high as an elastic limit is equally applied to all the blades 1'. After the above-mentioned setting is obtained, side edges of these blades are pressed and contacted with the work 2 while imparting a predetermined press force to the work, and the blades 1' are reciprocated in the longitudinal direction to cut the work while being supplied with a slurry processing or grinding fluid carrying abrasive grains in a liquid such as an oil or a water from a slurry supply part 5'.
Reciprocation is carried out by converting the rotation of a flywheel 11 into the linear motion of a connecting rod 2. The flywheel is rotated and driven through a V-shaped belt 14 from a motor 13.
The position of a pin fixed on the flywheel 11 which is engaged with the connecting rod 12 may be slidably adjusted, thereby to regulate the reciprocating velocity and stroke. The motor 13 may be, of course, driven at variable speed.
Thus, it is possible to provide many cut products at the same time. FIG. 9 shows an example of an apparatus in which a vertical flywheel is used. In this drawing, 6 is a spring, 15 is a weight and 16 is a powder tank. FIG. 10 shows another example wherein a lateral flywheel is used.
A cutting mechanism with free abrasive grains is shown in FIG. 12, wherein a processing fluid is supplied with abrasive grains into a gap between the blade 1 and the work 2 to roll and drag the abrasive grains by the relative motion therebetween, or to rub the work 2 with the abrasive grains, so that a fine breakage is generated in the work 2 to cause the cutting to be advanced. This method depends on a principle similar to that of the so-called lapping process.
The inherent advantages of the multi-blade cutting method with free abrasive grains are enumerated in the following points:
(1) A great number of large cut products may be simultaneously obtained.
(2) The processing or machining principle is similar to the lapping principle, so that the heat generated in processing is small and the abrasive grains may be used to provide a small stress layer.
(3) This cutting method is adapted to cut particularly hard and brittle materials, because of the lapping type cutting mechanism. Thus, the multi-blade cutting method with free abrasive grains is characterized by that large, hard and brittle materials may be simultaneously cut precisely into many parts.
As compared with the general cutting method for cutting the work with the above-mentioned bonded abrasive grains, or a disc grindstone, the work is processed extremely slowly.
Accordingly, the processing velocity per blade is considerably low as compared with the general grindstone cutting. Therefore, even if the work may be cut in this multi-blade cutting method, the time required in each cutting operation is considerably long as compared with the ordinary grindstone cutting, so that the cutting efficiency is not promoted as expected.
Under these conditions, this multi-blade cutting method is limited to be used only in the special materials field. In this cutting method, adding to the above-mentioned disadvantages, there are also various problems as described below.
Firstly, in this cutting method, since a large quantity of abrasive grains are mixed with the liquid to continuously supply a slurry of abrasive grains to the cutting part so as to dissipate about one-third the quantity of abrasive grains, it is impractical to use expensive super abrasive grains such as diamonds, CBN and the like, and only inexpensive abrasive grains of low hardness, such as SiC (GC) abrasive grains are commonly used. Consequently, the work to be cut is limited to relatively soft and brittle materials of Moore hardness of less than 7.
Secondly, this cutting method disfavored in view of the air pollution it causes because the apparatus and its surroundings generate a considerably nasty smell since the work is processed or machined while a slurry of free abrasive grains with oil and the like is supplied to the cutting part.
Moreover, this cutting method is similar to the lapping process in the processing principle, so that the work and blades are rubbed with the free abrasive grains of high hardness and this shortens the life of the blades. Consequently, the blades must be changed frequently and the apparatus is driven at a low processing speed and must be frequently stopped.
Also, when new materials which are recently developed and practised are cut, the blades are frequently exchanged during processing, and the cut surface of the work is changed in the exchange of the blades, which reduces the commercial values of cut products.
Thus, the multi-blade cutting method with free abrasive grains is not adapted to use in cutting of hard-to-machine new raw materials such as new ceramics, composite materials, and intermetallic compounds.